Pictured: The typical "skateboard" EV platform used by many manufacturers
Believe it or not, there’s quite a bit of internal and external mechanical differences between most major manufacturers' proprietary Hybrid vehicle and EV platforms, but the fundamentals typically remain the same. Here are some of the classifications and their respective acronyms:
Honda’s IMA ( Integrated Motor Assist ): Civic, Insight, & Accord
These setups have one single motor/generator placed between the ICE and the transmission, almost like a clutch or torque converter that is only used while accelerating to assist the engine while limiting fuel consumption. These vehicles use a traditional starter solenoid setup to crank the engine. The NiMh battery pack is not actively cooled, which leaves them prone to overheating and failure of the battery itself, and the inverter.
Toyota & Lexus Hybrid Synergy Drive
Toyota’s Hybrid Synergy Drive powertrain is in all Toyota and Lexus Hybrid platforms and uses both NiMh and Lithium-Ion based high voltage battery systems. Each system contains at least two motor generators in the transaxle and for AWD ( All Wheel Drive ) platforms, a separate electric rear drive unit - free of a drive shaft to help propel the vehicle in low traction scenarios. This level of Hybrid functionality allows for a temporary EV ( Electric Vehicle ) mode free of ICE operation while traveling under 45 mph and during light throttle application. The motor generators also work in tandem with the ICE to deliver greater throttle response and increased torque while reducing reliance on additional fuel consumption. These transaxles include a planetary gearset that is computer controlled to interact with the motor generators to produce a CVT ( Continuously Variable Transmission ) effect while accelerating. These types of transaxles are categorized as eCVTs.
Toyota and Lexus currently produce traditional Hybrid Vehicles and PHEVs
( Plug-In Hybrid Vehicles ), the latter having an energy dense lithium-ion high voltage battery capable of giving 40-50 miles of pure EV range before the ICE kicks in to compensate/charge and maintain the high voltage battery to a minimum level.
General Motors Hybrid and EV
General Motors has also been producing mild hybrids and full hybrids for quite some time. The most common systems seen are the eAssist mild hybrid BAS ( Belt - Alternator - Starter ) option on numerous GM platforms, and the 40 module NiMh Two-Mode hybrid Tahoe, Yukon, Escalade, Silverado, and Sierra. The Two-Mode was also used in certain Chevrolet Express cargo vans. The 1st and 2nd gen Chevrolet Volt and newer full EV, the Bolt use Lithium based batteries. The Volt is actually classified as a REX ( Range Extended ) EV due to the fact that the ICE inside the vehicle only charges the battery, specifically acting as a generator. This means that there is no physical mechanical connection between the engine and the drive axles. Only the Battery/Motor-Generator are able to drive the wheels. Another example of this would be the BMW i3 REX, which has a similar powertrain setup, albeit on a smaller scale.
Ford, Lincoln, Mercury
Most of Ford’s hybrid platforms use 4 cylinder based powertrains similar to Toyota in design and function, but have since moved on from NiMh to strictly Lithium based batteries. These are Atkinson cycle engines designed to maximize fuel economy, similar to what Toyota uses with two motor generators in the transaxle coordinating with a planetary gearset to produce a CVT driving characteristic, known as an eCVT ( Electronic Continuously Variable Transmission ). Recently Ford has begun to release full EVs. The new Mustang Mach E and Ford Lightning pickup truck are Ford’s first entries into full EV platforms using lithium batteries, at a relatively affordable price.
Tesla is the biggest household name in the EV car industry. Over time their initial offerings have evolved to include higher energy-density lithium batteries and extremely fast motor/generators as well as cooling systems designed to speed up battery charging to the fastest times available on just about any EV on sale today. The Model X and S share the same platform, while the Model 3 and Model Y share their own separate platform. The vehicles are designed with a skateboard-like structure with the battery packs being an integral part of the chassis in the vehicle. This provides a lower center of gravity, less body roll, and increased traction while cornering. All major manufacturers have adopted this design for their own respective EV projects.
To summarize, these days Lithium based batteries are the norm while NiMh is being phased out. This trend also coincides with most manufacturers moving towards full EV development as opposed to designing new hybrid platforms. Lithium is far more energy-dense than NiMh is, but also more costly to maintain as the cooling systems needed to prevent overheating and thermal runaway drive up the overall cost of high voltage batteries and the car itself.
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